Biomedical Engineering Reference
In-Depth Information
vivo
. Collagen-apatite nanocomposites assembled as microspheres have been
obtained in a water-in-oil emulsion condition. Spherical microparticles with
diameters ranging from tens to hundreds of micrometres were thus obtained.
Morphological studies showed that the nanostructured organisation of Ha
crystals was evenly distributed in the collagenic matrix. the nanocomposite
microspheres supported rat bone stem cell adhesion and growth and expressed
a series of genes that indicated their differentiation into osteoblasts. also, aLP
activity on the composite microspheres was higher than on control collagen
microspheres.
Antheraea pernyi silk fibroin (Ap-SF) has also been employed to control HA
nanocrystal formation (Ren
et al
., 2007). the mineral phase was formed under
relatively mild conditions, that is, incubation in a aqueous solution, pH 7.4 and
room temperature. an inorganic phase characterised by small carbonate-Ha
particles with low crystallinity has been shown to take place. Ultrastructural
studies have shown that these nanoparticles interacted with the fibroin to form
mineralised rod-like nanofibrils (4-5 nm in diameter). The composites were
shown to assemble into mineralised rods 49-74 nm in diameter.
Silk fibroin has been used to prepare HA nanocomposites using other
protocols. For example, silk fibroin can be used to produce HA-based
composites by a previous chemical modification of the protein with alkali
solution or enzyme digestion in an attempt to improve the interface between
the mineral and the organic matrix (Wang
et al
., 2007). Both pretreatments
favoured the formation of a highly ordered 3D porous network promoting
the preferential growth of Ha crystallites along the
c
-axis. in particular,
in the case of the enzyme treatment, the composite acquired a hierarchical
microstructure with higher degree of organization and more uniform pore size
distribution, where Ha crystallites underwent morphological transformation
from rod-like to whisker-like structures growing along the
c
-axis. the alkali
pretreatment induced more stable interactions between the biopolymer and
the forming Ha.
Alternatively, fibroin/HA composites were manufactured by alternating film
deposition in a lamination method where temperature and compression times
were varied (Kino
et al
., 2007). HA was deposited on fibroin films by soaking
methanol-treated fibroin films containing > 5 wt% CaCl
2
in SBF with an ion
concentration 1.5-fold higher than standard SBF. In the multilayered fibroin/
HA films obtained in this reiterated process, HA layers of an approximate
thicknesses of 3-5 mm were obtained. the bonding strength between the
fibroin and the HA layers was significantly affected by temperature and
compression time under the lamination method. the optimal conditions for
achieving the maximum t-peel strength and protein b-sheet contents were
determined to be 130°C for 4 min. the biocompatibility of the composites
when they were tested with cell line osteoblasts (MC3t3-E1) indicated good
substrate properties for the cells that were able to differentiate.
